Matthew 21:28-32 contains the story of two sons, one who said he would not do the work his father asked of him, yet did, and another who promised to work, but did not.
Jesus may have taken the theme of this parable from Isaiah 5:1-7, which some commentators call "The Song of the Vineyard." God pictures Israel and Judah as a vineyard. He does all He can for them, planting, protecting, and feeding them, but instead of the vineyard producing wonderful grapes, it produces wild grapes that are good for nothing. The reason: His people will not listen to Him. They promise to obey and give the appearance of belonging to Him, but they will not really work at it. Thus, they do not produce what God expected.
Who are the characters in the Parable of the Two Sons? The father is God. The first son, who flatly refuses to work in the vineyard, represents the weak, foolish, and base of this world (see I Corinthians 1:26-27). The second son, who promises to work yet never shows up, represents hypocrites, those who appear or profess one way but act another. The work the father asks them to do corresponds to living God's way of life.
The first son, who answers, "I will not," gives a carnal answer from a carnal mind. This is the mind all of us had before God called us out of the world. His answer displays no hypocrisy because he sincerely did not want to come under God's authority. He is guilty of bold rebellion.
The second son, who says, "I go," makes a promise that he never fulfills—and possibly never intends to fulfill. His word contradicts his performance. While his father is present, he conceals his determination to disobey; he is a liar. As Jesus says in Luke 6:46, "Why do you call me 'Lord, Lord,' and do not do the things which I say?" This son's guilt combines deception with disobedience.
In the parable both sons hear and respond verbally to their father's command, one negatively, one positively. The one who promises to obey but never follows through is just as guilty as if he had refused from the first. Though his promise to work may make him look good on the surface, his father will never accept his act of disobedience.
At this point, we have no reason to prefer one above the other; both are guilty of sin. However, their ultimate actions prove them different. After his blunt refusal, the first son repents of his sin and goes to work for his father. He sets his heart to do what his father wants. Though he promptly promises, the second son fails to perform. The first changes from bad to good, but the second does not change at all—if he makes any change, he goes from bad to worse!
Toward the end of the parable, Jesus poses the question: "Which of the two did the will of his father?" The obvious answer is he who repented and went to work. Then Jesus tells the Pharisees that the tax collectors and harlots would go in to His Kingdom before them because these blatant sinners believed and repented, while the "religious" people did not.
The warning to us is not to be a son who promises to work, then neglects to keep his word. God has called us, and we have accepted that calling, promising we would work. Now we must perform what we have promised.
We are living in the Laodicean era of God's church, and the effect of this is that many are letting down. Many are not faithfully keeping God's commandments and are neglecting His Sabbath and holy days. Church attendance is sporadic. Tithing is erratic. Too many have lost their zeal for God and His way of life, and they are veering away from the path to the Kingdom.
For many, things are going well, as they are indeed "rich and increased with goods" by this world's standards. Somehow, we equate this as God's approval, but God may well be patiently letting out rope so that we will either hang on to what God has given us or hang ourselves.